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Exam-style Questions: Transport

1. The roots of two groups of pea plants were placed in solutions containing radioactive potassium ions. For the experimental plants a respiratory inhibitor was added to the solution. At regular intervals the solutions surrounding the roots were tested for radioactive potassium ions. The table shows the results of this investigation.

Time from placing roots in solution/minutes

Concentration of radioactive potassium ions in the solutions surrounding the roots/arbitrary units

Experimental plants

Control plants

0

7.5

7.5

15

6.6

3.3

30

6.4

2.9

60

6.3

2.4

120

6.3

1.2

240

6.3

0.6

a)

(i) The rate of uptake of potassium by the experimental plants in the first 15 minutes was 0.06 units per minute.

Calculate the rate of uptake of potassium by the control plants over the same time period.

(ii) Suggest an explanation for the difference between the rates of uptake of the experimental and control plants in the first 15 minutes.

(iii) The rate of potassium ion uptake in the control plants in the first hour was faster than in the second hour. Suggest why.

b)

At the end of the investigation sections were cut across the stems of the pea plants and the amount of radioactivity measured. The diagram shows a section across the stem of a pea plant.

(i) Give one feature by which this section can be recognised as a stem.

(ii) Using a guideline, label and name the tissue in which you would expect to find the greatest amount of radioactivity.

cohesive forces insufficient to hold mercury up/mercury not cohesive to walls of xylem.

(4 marks)

(Marks available: 7)

3. Read the extract and then answer the questions which follow.

Fish breathe easy by putting the squeeze on blood cells
In the gills of a fish blood passes through structures called lamellae, two thin membranes held apart by cells which look like the pillars supporting a roof. Video recordings of this flow show that red blood cells become deformed as they pass between the pillar cells.

Normally the red blood cells of a trout are oval and measure 13.5 by 8.4 micrometres. As the cells flow through the lamellae, however, they stretch to more than 18 micrometres in length, and take the shape of a letter C or S. Some of the red blood cells get jammed between the pillar cells, blocking the progress of other blood cells.

This means that redblood cells passing through the gill lamellae travel about 50 per cent further than the shortest path. This helps to explain why fish gills are so good at picking up oxygen from water.

(Reproduced by permission of New Scientist)

a) The function of red blood cells is to transport oxygen. How is oxygen transported in red blood cells?

b) (i) Explain the advantage to the trout of the change in shape of its red blood cells as they pass through the gills.

(ii) Explain the advantage to the trout of some red cells getting jammed between the pillar cells.